This invention relates in general to radio data communication systems and more particularly to such systems capable of accommodating multiply and diverse signaling schemes or protocols operable within a single, unified communication network.
Radio data communications systems typically comprise a centrally located controller----i.e., Network Control Processor (NPC)----connected, such as by wire line, to a plurality of remote, but fixed RF transmitting stations, which collectively define the coverage for a given area/system. The NCP, in turn, is connected to and is controlled by a Host Computer.
The individual RF stations conventionally include a local controller----i.e., General Communications Controller (GCC)----and an associated transmitter/receiver (transceiver). The individual RF stations are all connected to the central NCP to thus form the particular Data Network which communicates with a plurality of portable/mobile (remote)radio data terminals transportable throughout the particular coverage area.
There are a number of particularized characteristics of such radio communication systems which distinguish then from the more conventional and widely known two-way radio voice communication systems. Although not specifically limited thereto, nevertheless, such radio data systems normally utilize two separate channels, namely, an inbound channel on which the remote terminals communicate with the central NCP, and an outbound channel on which the central NCP selectively communicates with the individual remote terminals.
In operation, the remote (portable/mobile) terminals monitor the outbound channel to determine whether any activity by others is occurring on the inbound channel. If not, the terminal is free to send its intended message on the inbound channel. If the remote terminal senses channel activity, it refrains from transmitting and retries later, usually on a random basis. To enable the remote terminal to determine whether or not there is channel activity, the NCP/GCC utilizes an inhibit signal comprising a stream of bits, termed "busy bits", which are appropriately embedded in the messages constituting the outbound channel message stream whenever a transmission is occurring on the inbound channel. If the busy bits are present, the operating channel for the remote terminal is deemed busy. If they are not present, the channel is deemed free for use (at least for contention). With this type of an arrangement, obviously the NCP/GCC must be sending a message continuously or nearly so on the outbound channel so that it may be frequently monitored for presence or absence of embedded busy bits. If the NCP is not sending specific messages to specific remote terminals, idle messages are employed in their stead.
Obviously, with the foregoing arrangement, there must be some manner of traffic control or rules of operation that must be implemented so as to enable efficient and effective operation. These operating rules may be considered as including a particular method or mode of signaling, encoding and decoding activities reading the transmitted received data, a method and means of accessing the associated operating channel, the rules for retry when access is denied, and possible acknowledgements back to the sending party when confirmation is wanted by the sending party regarding messages sent. Collectively, such rules combined in a particular way may be termed the "operating protocol" for the radio data system. Accordingly, until now, the particular system could only accommodate additional terminals/equipment that operated in the already established system protocol, either as "add-ons" to expand the system, or simply as replacement units.
As those skilled in the art are aware, time passes and new technologies and innovations result in significant improvements in all phases of system operation, and particularly with respect to more efficient and effective operating formats or protocols. It frequently proves advantageous for a manufacturer to redesign for any number of reasons, including by way of example and not limitation, message throughput, channel efficiency, cost----to name but a few. However, a significant user base may well have been established in the particular (old) signaling scheme which in the interest of economics and good business practice require such established formats or signaling protocols to be maintained and limit replacement products to those compatible therein. It would, of course, be desirable in the best interests of user economics as well as "customer satisfaction" to offer any new radio data products that are operable on the user's existing system----and then provide a graceful migration to "new" signaling scheme options. By graceful migration, it is meant the ability to offer a system upgrade capability to the existing user base that offers the demonstrable improvements of a "new" signaling format but does not require the wholesale replacement of existing and fully operational units as well as minimizing fixed network infrastructure changes with associated network downtime.